US2962620A - High frequency energy interchange apparatus - Google Patents

High frequency energy interchange apparatus Download PDF

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US2962620A
US2962620A US733328A US73332858A US2962620A US 2962620 A US2962620 A US 2962620A US 733328 A US733328 A US 733328A US 73332858 A US73332858 A US 73332858A US 2962620 A US2962620 A US 2962620A
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transmission line
electron
stream
slow wave
impedance
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US733328A
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Ward A Harman
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General Electric Co
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General Electric Co
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J25/00—Transit-time tubes, e.g. klystrons, travelling-wave tubes, magnetrons
    • H01J25/34—Travelling-wave tubes; Tubes in which a travelling wave is simulated at spaced gaps
    • H01J25/36—Tubes in which an electron stream interacts with a wave travelling along a delay line or equivalent sequence of impedance elements, and without magnet system producing an H-field crossing the E-field
    • H01J25/38—Tubes in which an electron stream interacts with a wave travelling along a delay line or equivalent sequence of impedance elements, and without magnet system producing an H-field crossing the E-field the forward travelling wave being utilised

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  • This invention relates to the class of devices which depend upon an interchange of energy between a stream of electrons and a radio frequency field to provide amplification and/or oscillations. More particularly, the invention relation to the class of high frequency energy interchange devices known as traveling wave tubes which include an electron gun for producing a stream of electrons in an interaction region and a radio frequency circuit or transmission line for producing radio frequency fields in the region of interaction, and the invention has for one of its principal objects the provision of improved methods and means for transferring high frequency energy between the radio frequency circuit and a wave guide or transmission line or the like and collecting electrons from the electron stream.
  • a major concern when utilizing generators or power sources is to obtain a maximum of power transfer from the generator to the desired load device. In other words, it is desirable to make the best use of power generated by the source. This is none the less true for generators and amplifiers in the microwave frequency spectrum such as traveling wave tubes.
  • the means of obtaining maximum power transfer between a traveling wave energy interchange device and its load must be dilierent from the means used in most devices which operate in lower frequency spectra, because a special type of transmission line, the slow wave transmission line, is used to obtain amplification and oscillations in the traveling wave device.
  • the slow wave transmission line is a crucial element in the traveling wave tube, the physical design dimensions of the slow wave structure take precedence over other considerations such as the characteristics of the load and transmission line external to the traveling wave device.
  • the slow wave circuit in a traveling wave tube is a helix which is made of conductive material.
  • the slow wave transmission line utilized in the traveling wave tube it is generally not practical to extend the slow wave transmission line utilized in the traveling wave tube out through the envelope to the load device. As a consequence, the energy must be brought out of the traveling wave tube and delivered to the load device by more conventional fast wave transmission line means; for example, a coaxial transmission line or hollow wave guide. If there is a discontinuity between the internal slow wave transmission line and the external fast wave transmission line, that is, if the impedance of one transmission line is appreciably different from the other transmission line at the junction between the two, backward traveling waves appear within the traveling wave tube due to reflections at the discontinuity. Such reflections interfere with operation of the traveling wave tube. For example, such reflections may cause power loss, loss of efiiciency and/or regeneration.
  • the problem of matching a slow wave helical transmission line to a fast wave transmission line, such as coaxial cable, is one of providing an impedance match between a transmission line having an impedance on the order of 300 to 400 ohms (the slow wave line) to a transmission "ice line having an impedance on the order of ohms (fast wave line).
  • the matching problem is not difficult for a particular frequency or a limited frequency range but the traveling wave tube is generally designed to operate over a broad range of frequencies and it is difiicult to obtain such an impedance match which is effective over the desired frequency range (e.g., 60 to 300 megacycles per. second).
  • Theparticular problem is not a new one and the match is generally accomplished by a means known as tapering the impedance. That is, the impedance 300 to 400 ohms is gradually tapered down or reduced over a length of the slow wave transmission line which is sufficiently long to minimize reflections in the frequency range of interest. When considering any individual frequency, such a match represents an engineering compromise.
  • the impedance taper when considered in connection with the output transmission line, must be accomplished in the region of the output portion of the device.
  • the portion of the slow wave circuit associated with the impedance taper is only partially effective for inter action with the stream and thus only partially effective in producing gainor amplification.
  • interaction is only partially effective in the region where the electron stream,
  • impedance tapering is ideally done in a region beyond that occupied by the electron stream because such an arrangement allows the shortest possible length .of electron stream for a given amplification or gain.
  • the electron stream It is important to keep the electron stream as short as possible since the stream is typically focussed by a mag ⁇ netic field supplied by a focussing solenoid or magnet. In either case, the focussing field producing apparatus is heavy and cumbersome. extra power supply is required. If the length of the electron stream is kept to a minimum, the size and weight of the focussing equipment can be kept to a minimum. There is the possibility of reducing the stream length from either end of the device; however, the electron gun and collector generally can not be placed within the region of outside the region occupied by the electron stream.
  • an object of the present invention is to provide a collector in a traveling wave tube of such a shape which will allow it to perform as a tapered impedance matching section as well as a collector for the electron stream and provide for a large percentage of the impedance tapering to be done beyond the point where the electron stream is collected.
  • typical half wave length of a helical slow wave transmission line at 60 megacycles is approximately 4 inches. If the tube is on the order of 24 inches long, the matching length represents about 30% of tube length at-this frequency. If the tapering portion of the slow wave circuit is 'done prior to collection of the electron stream, and the portion of the slow wave circuit in the impedance match area is substantially ineffective in providing interaction between the electron stream and the radio frequency waves, then the additional half a circuit wave length may be considered substantially wasted and the electron stream and tube are required to be at least half a circuit wave length longer.
  • a tapered impedance matching section is provided between the slow wave transmission line of a traveling wave energy interchange. device and a fast wave output transmission line which output tapered impedance match is accomplished by providing an electron collector and impedance match along the output end of the slow wave transmission line.
  • the physical size and position of the match-collector are arranged in such a manner that electrons from the stream are collected near the beginning of the impedance taper.
  • Figure l is a central, vertical, longitudinal section through a high frequency energy interchange device embodying one form of the present invention
  • Figure 2 is a transverse section through the tubular body of the device taken on line 2-2 of Figure 1;
  • Figure 3 is a side elevation showing one end of the high frequency energy interchange device with the envelope broken away to show only the slow wave struc ture and the collector-impedance match;
  • Figure 4 is a central, vertical, longitudinal section taken through a part of a high frequency energy interchange device employing another embodiment of the present invention
  • Figure 5 is a cross sectional view of the device of Figure 4 taken along section lines 55;
  • Figure 6 is a perspective view showing the impedance matching and electron collecting member utilized in the energy interchange device illustrated in Figure 4;
  • FIG. 7 is a partially broken away perspective view of still another energy interchange device which employs the present invention.
  • Figure 8 is a vertical longitudinal section of the embodiment of Figure 7.
  • a traveling wave tube 10 is provided with a long cylindrical (circular cylinder) envelope 11 which is evacuated and sealed.
  • the envelope 11 houses an electron stream producing electron gun 12 at one end which produces and directs a hollow cylindrical stream of electrons 13 down the length of the envelope 11.
  • the envelope 11 also encloses a slow wave transmission line 14 which is illustrated as being a helical strip of conducting material, and an electron collector and impedance matching member 15.
  • the electron collector and impedance matching member 15 is positioned at the opposite end of the electron tube from the electron gun 12, and the slow wave transmission line extends substantially throughout the region between the extreme outer end of the collector 1-5 4 and the electron gun 12.
  • the physical configuration and relative location of the slow wave transmission line 14, the electron stream 13, the collecting and impedance matching member 15, and the envelope 1]. may best be seen by an inspection of Figures 2 and 3 in connection with Figure 1.
  • the electron stream 13 produced by the electron gun 12 is directed down the length of the interaction region in close proximity to the slow wave transmission line 14. Residual energy in the electron stream is collected on the collector and impedance matching member 15.
  • the electron stream 13 and electromagnetic waves propagated down the slow wave transmission line 14 interact to provide gain or amplification in the fashion typical to traveling wave tubes. That is to say that the radio frequency waves propagated along the transmission line 14 interact with electrons in the electron stream 13 to cause a redistribution in the form of partial bunching along the stream.
  • the inverse phenomenon occurs and the bunched stream induces fields and cur rents upon the helix.
  • the amplitude of the radio frequency waves increases along the helix because the electron stream gives up more energy to the helix than it abstracts therefrom. Consequently an amplification of the radio frequency waves on the helix takes place.
  • the traveling wave tube illustrated is shown somewhat sketchily. It is felt that more detail is not necessary since many of the elements of the traveling wave tube are common to traveling wave tubes in general and are not novel per se and further, the particular tube design shown is illustrated and discussed in a paper entitled A C-W UHF TWT Power Amplifier of Extended Band Width, by Ward A. Harman, published on pages 36 through 40, inclusive, of the 1957 Proceedings of the National Conference on Aeronautical Electronics, sponsored by the Institute of Radio Engineers, on May 13, 14 and 15, 1957, in Dayton, Ohio.
  • the electron gun 12 which produces the hollow electron stream 13 is illustrated in block form since it is a conventional hollow stream gun known in the art as a Pierce type gun for rectilinear flow.
  • Harman article supra illustrates and describes the electrode and gun configuration on page 39 and it is felt a detailed description of the particular gun is not warranted. This is particularly true since any hollow stream electron gun could be used in the particular application.
  • Other hollow stream guns which might be used are illustrated and described on pages through 163 of the book by Willis W. Harman entitled Fundamentals of Electronic Motion published by the McGraw-Hill Book Company 1953.
  • a series of conductive leads 16 are brought into the envelope 11 and connected to various electrodes (not shown) of the gun 12 in order to establish the appropriate electrode potentials to cause the formation and projection of the electron stream 13 down the axis of the device 10.
  • Projecting tabs 17 extend outwardly from the outer periphery of the gun and rest against the inner wall 11 of the vacuum tube 10 and are provided in order to center the gun 12 within the vacuum tube and help hold it in position The conductive leads 16 also help hold the gun 12 in position.
  • Focussing is provided by producing a magnetic field axially along the structure. This is typically accomplished by providing a long annular solenoid which surrounds the entire tube. To simplify the present drawing and description, the magnetic field producing solenoid is not illustrated.
  • the helical transmission line 14 is co axially positioned within the glass envelope 11 by means of glass spacing rods 25 which are spacedequidistant inside the glass envelope 11 in such a manner that they extend longitudinally along the wall over the region occupied by the helix 14.
  • the particular main circuit or beam helix 14 illustrated is designed to operate in the UHF band between approximately 60 and 300 megacycles. As was previously indicated, it is not practical to scale the circuit length from higher frequency models. For the band of frequencies desired, a circuit length of approximately 2 feet was found to be practical with the thin hollow stream of electrons 13 located very close to the circuit.
  • Radio frequency waves are introduced onto the circuit 14 by means of a conductor 18 brought in to the vacuum tube 11 at the gun end of the tube and the amplified energy is abstracted from the beam helix by means of a coaxial cable 19 near the opposite end of the tube 11.
  • the coaxial cable 19 has an outer conductor 20 connected to the collector 15 and a central inner conductor 21 connected directly to the last turn of the beam helix 14.
  • the interior of the coaxial transmission line 19 is provided with a dielectric window 24 which allows propagation of radio frequency energy down the line but provides a vacuum tight seal.
  • the impedance of the relatively high impedance beam helix 14 (on the order of 400 ohms) is matched to the relatively low impedance coaxial cable 19 (on the order of 50 ohms) using the collectorimpedance match member 15. It is well known that matching two impedances of such disparate values may be accomplished by providing a section wherein the impedance varies continuously, or at least in very small steps, between the two extreme values. This arrangement is known as a tapered impedance or tapered transmission line.
  • the impedance matching and electron collector member 15, which is used to match the impedance between the slow wave helical transmission line 14 and the output coaxial cable 19 is substantially ogival in shape.
  • the collector member is inserted within the slow wave transmission line 14 in such a manner that its axis of revolution, or its central axis, is coincident with the longitudinal axis of the helical transmission line 14 and evacuated envelope 11.
  • the external configuration of the tapered impedance matching member is shaped so that the impedance of the transmission line 14 varies over the matching portion in an exponential cosine fashion as described in the Lund article supra.
  • the external configuration of the matching section may be varied in any way to obtain any of the desired impedance tapers described in the articles cited above.
  • the fact that the matching member is a frustum is not crucial since the nose portion of the member is far enough removed from the transmission line 14 that it does not effect the impedance appreciably.
  • the impedance matching collector member 15 is held in position within the vacuum envelope 11 by means of a cylindrical supporting section 23 which is coaxially arranged and fixed to a disk shaped annular back wall member 22 which extends inwardly from the periphery of the back or large end of the collector 15.
  • the cylindrical supporting member 23 for the collector 15 is held in the glass envelope 11 by a vacuum tight seal around its outer periphery.
  • the entire matching member 15 is held in position within the envelope and its interior is open to the atmosphere to provide a large cooling surface so the residual energy of the electron stream does not overheat the collector 15.
  • the open interior of collector 15 provides space for a coolant to be circulated without affecting the electrical design of the device where it is necessary to provide additional cooling.
  • the arrangement illustrated allows the full impedance of the slow wave transmission line to be maintained over nearly the entire length of the electron stream, thus preventing possible degradation in efficiency as a result of reducing transmission line impedance over the final output section of the high frequency energy interchange device.
  • FIGS 4, 5 and 6 illustrate a portion of a high frequency energy interchange device 30 employing another embodiment of the invention. Only the collector end of a high frequency energy interchange device 30 is illustrated in this figure in order to simplify the description and drawing.
  • the energy interchange device 30 includes a cylindrical or tubular metallic envelope 31 which is evacuated and sealed.
  • the envelope 31 encloses a helical slow wave transmission line 32, an electron collector and impedance matching member 33 which surrounds the collector end of the slow wave transmission line 32,
  • the interaction region for the device 30 is outside of the helical transmission line 32.
  • the electron stream 34 and electromagnetic waves propagated down the slow Wave transmission line 32 interact to provide gain or amplification in the same manner described with respect to the device 10 of Figure
  • the helical slow wave transmission line .32 is wound on I a supporting dielectric cylinder 35 which is also utilized to hold the helix in Position within the evacuated envelope 31.
  • An annular groove 36 which is concentric with the outer wall of the envelope and just large enough to hold one end of the dielectric helix supporting cylinder 35, is provided in the end wall 37.
  • the end of cylinder 35 is then positioned in the annular groove 36 so that the helix is held coaxially within the evacuated envelope 31.
  • the impedance matching and electron collecting member 33 is positioned coaxially with respect to the circuit helix 32 and externally thereof so that it collects the electrons from the stream 34 near the output end of the device 30.
  • the collector matching member 33 best seen in Figures 4 and 6, has a shape designed to give the desired impedance taper at the output end of the slow wave transmission line 32 as described in connection with the slow wave transmission line 14 in the embodiment illustrated in Figure 1.
  • the shape of the matching member is generally that of the bell or horn of a trumpet.
  • the open end (i.e., the end having the largest diameter) of the matching member 33 is directed toward the electron gun end of the device 30.
  • the end of the impedance matching member which is closest to the electron gun is farthest away from the transmission line 32 so that it has the least effect upon the impedance of the line and the end of the matching member 33 which is nearest the collector end of the tube is very close to the transmission line 32 so that it has the maximum effect on the impedance of the line and reduces the impedance to some value which corresponds to the impedance of the particular fast wave transmission line 38 which abstracts power from the device and for which the transmission was designed.
  • the impedance matching and collector member 33 is held in position in the envelope 31 at both ends.
  • the largest end of the impedance matching member 33 is held in position by the tubular envelope 31. This is accomplished by making the outer circumference of the open end of the matching member 33 of such a size as to fit closely within the inner periphery of the cylindrical envelope 31.
  • the smaller end of the matching member 33 is inserted in an annular groove 43 which is concentric with the outer wall of the evacuated envelope 31.
  • the impedance matching member is held in position within the evacuated envelope 31 and both ends may be brazed to the metallic wall to form a seal. If such seals are provided, a coolant may be circulated around the external surface of the collector member 33 without affecting operation of the device.
  • the particular fast wave transmission line 38 used to abstract power from the device 30 is a conventional coaxial transmission line which has an outer conductive sheath 39 and an inner conductor 40 separated by a dielectric insulation 42.
  • the coaxial transmission line is also provided with a dielectric window 41 which acts as a seal to prevent deterioration of the vacuum within the energy interchange device 39 and to transmit electromagnetic waves abstracted from the high frequency energy interchange device 30.
  • the coaxial cable 38 is brought into the energy interchange device 30 through the end wall 37 and the collector matching member 33.
  • the outer conductive sheath 39 of the coaxial cable 38 is electrically connected to both the envelope 31 and the collector impedance match member 33 while the inner conductor 40 is connected to the helix 32.
  • power is abstracted from the high frequency energy interchange device 30 by the fast wave transmission line 38.
  • the hollow electron stream 34 is collected on the front portion of the tapered vimpedancematching section, thus a lowing most of the impedance matching to be done beyond the point of collection of electrons from the stre;m.
  • This arrangement eliminates the necessity of providing a separate collector beyond the helical slow wave transmission line 32 and a separate impedance matching section. Consequently, substantially the full length of the electron stream 34 is available for interaction with the slow wave structure 32.
  • the region which must be occupied by an electron stream focussing field is reduced to a minimum. This means that the amount of equipment required to produce this field is also reduced to a minimum.
  • matching by conventional means is accomplished over a region which includes both the transmission line and the electron stream. Consequently, the slow wave transmission line impedance is lowered over the region where the maximum transfer of energy from the electrons to the circuit would otherwise take place.
  • Figures 7 and 8 illustrate the invention as appplied in a linear sheet stream type high frequency energy interchange device 45.
  • the elements utilized in the device 45 correspond to the elements in the devices illustrated in Figures 1 and 4 and the basic interaction mechanism of the apparatus disclosed in Figures 7 and 8 does not differ in any fundamental respects. However, the construction of the elements of the devices are somewhat different. Consequently, the impedance matching and electron stream collecting members differ in geometrical configuration.
  • the device 45 includes an enclosed and evacuated envelope 46 having a rectangular cross section.
  • Envelope 45 encloses a transmission line 47 of the type referred to as a zig-zag slow wave circuit, a sheet stream producing electron gun 48 at one end, and an impedance matching and electron-collecting member 49 at the opposite end of the device.
  • the electron gun 48 pro Jerusalem and directs a sheet-like stream of electrons 50 down the length of the envelope 46 beneath and in close proximity to the zig-zag slow wave circuit 47 and the electrons are collected at the opposite end of the device on the collector and matching member 49.
  • the electron stream 5i and the electromagnetic Waves propagated down the zigzag slow wave circuit 47 interact to produce amplification in a manner similar to that described with respect to the device 1% of Figure l.
  • the electron gun 48 is illustrated rather diagramatically since it is a conventional gun for producing rectilinear electron flow.
  • the gun includes a cathode member 51 with an electron emissive surface 52, two pairs of electron focussing and directing electrodes 53 and 54, respectively, and heater elements which are not shown.
  • Each of the pairs of electron focussing and directing electrodes 53 and 54 includes two substantially planar, rectangular conductive plates spaced far enough apart to allow the rectilinear stream of electrons 50 to pass between them and are sloped to insure that the electron accelerating and directing electric fields therebetween have the desired configuration.
  • the design considerations for a gun of the type illustrated are discussed in the book entitled Theory and Design of Electron Beams 2nd edition by J. R.
  • the substantially planar zig-Zag slow wave circuit 47 is suspended with its plane generally horizontal and parallel to the plane of the sheet electron stream 50 by means of insulating supporting strips 55 which extend down the full length of the energy interchange device 45.
  • a pair of strips 56 is provided along each side of the device; however, it is not convenient to illustrate both pairs of strips in either Figures 7 or 8.
  • the strips are all identical, are generally L-shaped in cross section and are arranged in the same general manner on opposite sides of the device.
  • the pair of slow wave circuit supporting insulating strips 56 are arranged along one side wall of the envelope 46 in such a manner that the legs of the Us mate to support one edge of the slow wave circuit 47.
  • the particular device illustrated operates as a forward wave amplifier.
  • the radio frequency energy is introduced onto the slow wave circuit 47 by means of a coaxial transmission line 57 at the gun end of the device and the amplified radio frequency energy is abstracted by means of the coaxial transmission line 58 at the collector end.
  • the input coaxial transmission line 57 includes a center conductor 59 which is connected to the input end of the slow wave transmission line and an outer conductive sheath 60 Which is brought into the energy interchange device and connected to an input impedance matching conductive member 62.
  • the output coaxial conductor 58 includes an inner conductor 61 which is connected directly to the slow wave transmission line 47 at its output end and an outer conductive sheath 65 which is connected to the output impedance matching and collector member 49.
  • Impedance matching members 49 and 62 are of substantially identical geometrical configuration although, as illustrated, the size of the two members may differ.
  • the portion of the members which accomplishes the matching function is the conductive surfaces 63 and 64- respectively, which are best described as having generally parabolic shapes when viewed from the side (see Figure 8).
  • the shape is not necessarily derived from any known geometrical figures but is designed to give the desired transition in impedance between the transmission lines under consideration.
  • the proper impedance match is accomplished between the coaxial transmission line 57 at the gun end of the tube by positioning the matching member 62 in such a manner that its conductive surface is near the zigzag transmission line 47 near the gun end and slopes away from the circuit.
  • the impedance of the slow wave transmission line 47 is low (about 50 ohms) near the gun end and is approximately that of the coaxial transmission line 57.
  • the collector impedance match member 49 is relatively far from the slow wave circuit 47 at the end Where it collects electrons and is very near the slow wave circuit near the coaxial transmission line 58.
  • the electron stream 50 is collected on the front portion of the collector 49 where the collector has little effect on the impedance of the slow wave circuit 47. Consequently, most of the impedance matching is done beyond the point of collection of electrons in the stream. As a result, substantially the full length of the stream 50 is available for interaction with the slow wave circuit 47.
  • Both of the matching members 49 and 62 are illustrated as solid members. This is done because it is a simple construction and such members can easily be brazed to the walls of the envelope 46. However, the
  • matching members may be made hollow to provide for coolant or of any other desired construction.
  • the high frequency energy interchange devices 10, 30 and 45 are all illustrated as forward wave amplifiers. It is to be particularly understood that the principles set forth are equally applicable to backward Wave ampli-t tiers and forward and backward wave oscillators. It should also be understood that the invention is equally applicable to cylindrical devices as well as the linear models illustrated.
  • a high frequency energy interchange device including an evacuated envelope, a slow wave transmission line positioned within said envelope, an electron stream producing means positioned at one end of said evacuated envelope for producing a stream of electrons in the axial direction within said evacuated envelope and in close proximity to said slow wave transmission line, input and output fast wave transmission lines connected to said slow Wave transmission line to introduce radio frequency energy thereon and abstract radio frequency energy therefrom respectively, and an impedance matching electron stream collecting means positioned within the end of said evacuated envelope opposite the electron stream producing means and in the path of the electron stream, said stream collecting means having a collecting surface coextensive with a portion of said transmission line which surface is closest to said transmission line at its end which is furthest removed from said electron stream producing means and tapers away from said transmission line at its end which is nearest said electron gun producing means in such a manner that the electron stream is intercepted along the length of the said stream collecting means whereby the impedance of said slow wave transmission line is gradually reduced and residual energy in said electron stream is dissipated in the region where the
  • a high frequency energy interchange device including an evacuated envelope, a slow wave transmission line positioned within said envelope, an electron stream producing means positioned at one end of said evacuated envelope for producing a stream of electrons in the axial direction within said evacuated envelope and in close proximity to said slow wave transmission line, input and output fast wave transmission lines connected to said slow wave transmission line to introduce radio frequency energy thereon and abstract radio frequency energy therefrom respectively, and an elongated impedance matching electron collecting member positioned in the path of the electron stream near said slow wave transmission line within the end of said envelope opposite the electron stream producing means, said impedance matching electron collecting member extending along the length of said slow wave transmission line at least one half circuit wave length for the lowest frequency in the band of frequencies under consideration and having an electron collecting surface which is farthest from said slow wave.
  • a high frequency energy interchange device including an evacuated envelope, a coiled slow wave transmission line positioned within said envelope along the longitudinal axis thereof,
  • an electron stream producing means positioned at one end of said evacuated envelope for producing a stream of electrons in the axial direction within said evacuated envelope and said coiled slow wave transmission line, input and output fast wave transmission lines connected to said coiled transmission line to introduce radio frequency energy thereon and abstract radio frequency energy therefrom respectively, and an impedance matching electron stream collecting means coaxially positioned adjacent the end of said coiled slow wave transmission line opposite the electron stream producing means, said impedance matching means arranged to extend over a portion of the same region as said transmission line and have its end which is closest to said electron producing means the greatest distance from said transmission line for performing the functions of gradually reducing the impedance of said coiled slow wave transmission line and dissipating residual energy in said electron stream.
  • a high frequency energy interchange device including an evacuated envelope, a coiled slow wave transmission line positioned within said envelope along the longitudinal axis thereof, an electron stream producing means positioned at one end of said evacuated envelope for producing a stream of electrons in the axial direction within said evacuated envelope and said coiled slow wave transmission line, input and output fast wave transmission lines connected to said coiled transmission line to introduce radio frequency energy thereon and abstract radio frequency energy therefrom respectively, and an elongated impedance matching electron collecting member positioned within the end of said helical transmission line opposite the electron stream producing means and extending at least one half circuit wave length for the lowest frequency in the band of frequencies under consideration, said impedance matching electron collecting member having an externai surface of revolution which has its smallest diameter nearest the electron stream producing means.
  • a high frequency energy interchange device including an evacuated envelope, a coiled slow wave transmission line positioned within said envelope along the longitudinal axis thereof, an electron stream producing means positioned at one end of said evacuated envelope for producing a stream of electrons in the axial direction within said evacuated envelope and outside said coiled slow wave transmission line, input and output fast wave transmission lines connected to said coiled transmission line to introduce radio frequency energy thereon and abstract radio frequency energy therefrom, respectively, and an elongated impedance matching electron collecting member positioned around the end of said helical transmission line opposite the electron stream producing means and extending at least one half circuit wave length for the lowest frequency in the band of frequencies under consideration, said impedance matching electron collecting member having a collecting surface of revolution which has its largest diameter nearest the electron stream producing means.
  • a high frequency energy interchange device including an evacuated envelope, a substantially planar slow wave transmission line positioned within said envelope along the length thereof, an electron stream producing means positioned at one end of said evacuated envelope for producing a sheet stream of electrons in the axial direction within said evacuated envelope in close proximity to said slow wave transmission line, input and output fast wave transmission lines connected to said slow wave transmission line to introduce radio frequency energy thereon and abstract radio frequency energy therefrom respectively, and an elongated impedance matching electron collecting member positioned adjacent the end of said slow wave transmission line opposite the electron stream producing means in the path of the stream and extending along said slow wave transmission line at least one half circuit wave length for the lowest frequency in the band of frequencies under consideration, said impedance matching electron collecting member having an electron collecting surface which is farthest from said slow wave transmission line nearest the electron stream producing means and tapers toward said transmission line.
  • a high frequency energy interchange device including in combination an evacuated envelope, a substantially planar slow wave transmission line positioned within said envelope, an electron stream producing means for producing a sheet stream of electrons in the axial direction within said envelope in close proximity to said slow wave transmission line, input and output fast wave transmission lines connected to said slow wave transmission line to introduce radio frequency energy thereon and abstract radio frequency energy therefrom respectively, and an impedance matching electron stream collecting means positioned within the end of said envelope opposite the electron stream producing means for performing the functions of gradually reducing the impedance of said slow wave transmission line and dissipating residual energy in said electron stream, said electron stream collecting means including a collecting surface coextensive with the portion of said slow wave transmission line which surface is closest to said transmission line at its end which is furtherest removed from said electron stream producing means and tapers away from the transmission line at its end which is nearest said electron stream producing means.
  • an evacuated envelope a helical slow wave transmission line coaxially positioned within said envelope, an electron stream producing means for producing a hollow stream of electrons in the axial direction within said helical transmission line in close proximity thereto, input and output fast wave transmission lines connected to said helical transmission line to introduce radio frequency energy thereon and abstract radio frequency energy therefrom, respectively, and an elongated impedance matching electron collecting member positioned within the end of said transmission line opposite said electron gun, said impedance matching member having a length of at least one half circuit wave length for the lowest one of the band of frequencies under consideration and having a surface of revolution which has its end with the smallest diameter directed toward said electron gun and peripheral dimensions of such proportions that electrons from the stream are collected adjacent a high impedance region of said slow wave transmission line.
  • an evacuated envelope a helical slow wave transmission line coaxially positioned within said envelope, an electron stream producing means for producing a hollow stream of electrons in the axial direction within said envelope in close proximity to said slow wave transmission line, input and output fast wave transmission lines connected to said helical transmission line to introduce radio frequency energy thereon and abstract radio frequency energy therefrom respectively, and an elongated impedance matching electron collecting member coaxially positioned within the end of said envelope opposite said electron gun, said impedance matching member extending along the length of said slow wave transmission line a distance of at least one half circuit wave length for the lowest one of the band of frequencies under consideration and having a surface of revolution which has its end which is farthest away from said slow wave transmission line directed toward said electron gun and peripheral dimensions of such proportions that electrons from the stream are collected adjacent a high impedance region of said slow wave transmission line.
  • an evacuated envelope a slow wave transmission line positioned within said envelope, an electron stream producing means for producing a sheet stream of electrons in the axial direction within said envelope in close proximity to said slow wave transmission line, input and output fast wave transmission lines connected to said slow wave transmission line to introduce radio frequency energy thereon and abstract radio frequency energy therefrom respectively, and an elongated impedance matching electron collecting member positioned adjacent the end of said slow wave transmission line opposite said electron gun, said impedance matching member having a length of at least one half circuit wave length for the lowest one of the band frequencies under consideration and having a surface which varies in distance from said slow wave transmission line in such a manner that its end which is directed toward said electron gun is farth est removed from said slow wave transmission line and electrons from the stream are collected adjacent a high impedance region of said slow wave transmission line.
  • an electron stream collecting tapered impedance matching member located within the end of the device opposite the electron stream producing gun with the portion farthest removed from the transmission line directed toward the gun and extending along the length of the transmission line.
  • a combination electron collector impedance matching member for use in a high frequency energy interchange device which depends upon the interaction of an electron stream with electromagnetic waves propagated down a transmission line in close proximity to the electron stream, the said electron collecting impedance matching member positioned adjacent the slow wave transmission line and comprising a conductive member having a tapered surface which extends at least one-half circuit wave length along the transmission line with its end which is the greatest distance away from the transmission line directed toward the source of electrons.
  • a substantially ogival shaped electron stream collecting impedance matching member located within the end of the helical transmission line opposite the electron stream producing gun w.th the portion having the smallest diameter directed toward the gun.
  • a combination electron collector impedance matching member for use in a high frequency energy interchange device which depends upon the interaction of a hollow electron stream with electromagnetic waves propagated down a helical transmission line inside the electron stream, the said electron collecting impedance matching member comprising a conductive member having a tapered surface of revolution extending at least one-half circuit wave length around one end of the helical transmission line with its largest end directed toward the source of electrons.
  • a high frequency energy interchange device including an evacuated envelope, a coiled slow wave transmission line positioned within said envelope along the longitudinal axis thereof, an electron stream producing means positioned at one end of said evacuated envelope for producing a stream of electrons in the axial direction with said evacuated envelope and said coiled slow wave transmission line, input and output fast wave transmission lines connected to said coiled transmission line to introduce radio frequency energy thereon and abstract radio frequency energy therefrom respectively, and an elongated impedance matching electron collecting member having an external surface of revolution which is generally ogival positioned in the end of said helical transmission line opposite the electron stream producing means in such a manner that the end of reduced diameter is directed toward said electron stream producing means, said impedance matching member having a length corresponding to at least one-half circuit wave length for 14 the lowest frequency of the band of frequencies under consideration.
  • a high frequency energy interchange device including in combination an evacuated envelope, a helical slow wave transmission line coaxially positioned within said envelope, an electron stream producing means for producing a hollow stream of electrons in the axial direction within said helical transmission line in close proximity thereto, input and output fast wave transmission lines connected to said helical transmission line to introduce radio frequency energy thereon and abstract radio frequency energy therefrom respectively, and a substantially ogival shaped conductive impedance matching electron stream collecting means positioned within the end of said helical slow wave transmission line opposite the electron stream producing means for performing the functions of gradually reducing the impedance of said helical slow wave transmission line and dissipating residual energy in said electron stream.
  • an evacuated envelope a helical slow wave transmission line coaxially positioned within said envelope, an electron stream producing means for producing a hollow stream of electrons in the axial direction within said helical transmission line in close proximity thereto, input and output fast wave transmission lines connected to said helical transmission line to introduce radio frequency energy thereon and abstract radio frequency energy therefrom respectively, and an elongated impedance matching electron collecting member having a substantially ogival conductive surface positioned within the end of said transmission line opposite said electron gun with its end having the smallest diameter directed toward said electron gun, said impedance matching member having a length of at least one-half circuit wave length for the lowest one of the band of frequencies under consideration and peripheral dimensions of such proportions that electrons from the stream are collected adjacent a high impedance region of said slow wave transmission line.
  • an electron stream collecting impedance matching member having a shape defined by the frustum of an ogive located within the end of the helical transmission line opposite the electron stream producing gun with the portion having the smallest diameter directed toward the gun.
  • a high frequency energy interchangedevice including an evacuated envelope, a helical slow wave transmission line positioned coaxially within said envelope, a hollow electron stream producing means positioned at one end of said evacuated envelope for producing a stream of electrons in the axial direction within said evacuated envelope and external to said slow wave transmission line, input and output fast wave transmission lines connected to said helical transmission line to introduce radio frequency energy thereon and abstract radio frequency energy therefrom respectively, and an elongated impedance matching electron collecting member having an internal surface of revolution which is substantially defined by the frustum of a hyperboloid positioned surrounding the end of said helical transmission line opposite the electron stream producing means in such a manner that the end of greatest diameter is directed toward said electron stream producing means, said impedance matching member having a length corresponding to at least one-half circuit wave length for the lowest frequency of the band of frequencies under consideration.
  • an evacuated envelope a helical slow wave transmission line coaxially positioned within said enaseaeao 15 velope, an electron stream producing means for producing a hollow stream of electrons in the axial direction within said helical transmission line in close proximity thereto, input and output fast wave transmission lines connected to said helical transmission line to introduce radio frequency energy thereon and abstract rad-i0 frequency energy therefrom respectively, and an elongated impedance matching electron collecting member having a conductive surface defined by the frusturn of an ogive positioned within the end of said transmission line 0pposite said electron gun with its end having the smallest diameter directed toward said electron gun, said impedance matching member having a length of at least one-half circuit wave length for the lowest one of the band of frequencies under consideration and peripheral dimensions of such proportions that electrons from the stream are collected adjacent a high impedance region of said slow wave transmission line.

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Description

N 1960 w. A. HARMAN HIGH FREQUENCY ENERGY INTERCHANGE APPARATUS 3 Sheets-Sheet 1 Filed May 6, 1958 WAPD A. HARMAN INVENTOR.
Nov. 29, 1960 w. A. HARMAN 2,962,620
HIGH FREQUENCY ENERGY INTERCHANGE APPARATUS Filed iviay 6, 1958 5 SheetsSheet 2 WAPD A. HAEMAN INVENTOR.
in I {"21 BY Nov. 29, 1960 w. A. HARMAN HIGH FREQUENCY ENERGY INTERCHANGE APPARATUS 3 Sheets-Sheet 5 Filed May 6, 1958 WARD A. HARMAN INVENTOR.
Anon/5 HIGH FREQUENCY ENERGY INTERCHANGE APPARATUS Ward A. Harman, Palo Alto, Calif., assignor to General Electric Company, a corporation of New York Filed May 6, 1958, Ser. No. 733,328
20 Claims. (Cl. 315-35) This invention relates to the class of devices which depend upon an interchange of energy between a stream of electrons and a radio frequency field to provide amplification and/or oscillations. More particularly, the invention relation to the class of high frequency energy interchange devices known as traveling wave tubes which include an electron gun for producing a stream of electrons in an interaction region and a radio frequency circuit or transmission line for producing radio frequency fields in the region of interaction, and the invention has for one of its principal objects the provision of improved methods and means for transferring high frequency energy between the radio frequency circuit and a wave guide or transmission line or the like and collecting electrons from the electron stream.
' A major concern when utilizing generators or power sources is to obtain a maximum of power transfer from the generator to the desired load device. In other words, it is desirable to make the best use of power generated by the source. This is none the less true for generators and amplifiers in the microwave frequency spectrum such as traveling wave tubes. The means of obtaining maximum power transfer between a traveling wave energy interchange device and its load must be dilierent from the means used in most devices which operate in lower frequency spectra, because a special type of transmission line, the slow wave transmission line, is used to obtain amplification and oscillations in the traveling wave device. Since the slow wave transmission line is a crucial element in the traveling wave tube, the physical design dimensions of the slow wave structure take precedence over other considerations such as the characteristics of the load and transmission line external to the traveling wave device. In its most common form, the slow wave circuit in a traveling wave tube is a helix which is made of conductive material.
It is generally not practical to extend the slow wave transmission line utilized in the traveling wave tube out through the envelope to the load device. As a consequence, the energy must be brought out of the traveling wave tube and delivered to the load device by more conventional fast wave transmission line means; for example, a coaxial transmission line or hollow wave guide. If there is a discontinuity between the internal slow wave transmission line and the external fast wave transmission line, that is, if the impedance of one transmission line is appreciably different from the other transmission line at the junction between the two, backward traveling waves appear within the traveling wave tube due to reflections at the discontinuity. Such reflections interfere with operation of the traveling wave tube. For example, such reflections may cause power loss, loss of efiiciency and/or regeneration.
The problem of matching a slow wave helical transmission line to a fast wave transmission line, such as coaxial cable, is one of providing an impedance match between a transmission line having an impedance on the order of 300 to 400 ohms (the slow wave line) to a transmission "ice line having an impedance on the order of ohms (fast wave line). The matching problem is not difficult for a particular frequency or a limited frequency range but the traveling wave tube is generally designed to operate over a broad range of frequencies and it is difiicult to obtain such an impedance match which is effective over the desired frequency range (e.g., 60 to 300 megacycles per. second). Theparticular problem is not a new one and the match is generally accomplished by a means known as tapering the impedance. That is, the impedance 300 to 400 ohms is gradually tapered down or reduced over a length of the slow wave transmission line which is sufficiently long to minimize reflections in the frequency range of interest. When considering any individual frequency, such a match represents an engineering compromise.
The impedance taper, when considered in connection with the output transmission line, must be accomplished in the region of the output portion of the device. However, the portion of the slow wave circuit associated with the impedance taper is only partially effective for inter action with the stream and thus only partially effective in producing gainor amplification. Thus, interaction is only partially effective in the region where the electron stream,
is most effective in producing a transfer of energy. In view of this fact, impedance tapering is ideally done in a region beyond that occupied by the electron stream because such an arrangement allows the shortest possible length .of electron stream for a given amplification or gain.
It is important to keep the electron stream as short as possible since the stream is typically focussed by a mag{ netic field supplied by a focussing solenoid or magnet. In either case, the focussing field producing apparatus is heavy and cumbersome. extra power supply is required. If the length of the electron stream is kept to a minimum, the size and weight of the focussing equipment can be kept to a minimum. There is the possibility of reducing the stream length from either end of the device; however, the electron gun and collector generally can not be placed within the region of outside the region occupied by the electron stream.
Accordingly, an object of the present invention is to provide a collector in a traveling wave tube of such a shape which will allow it to perform as a tapered impedance matching section as well as a collector for the electron stream and provide for a large percentage of the impedance tapering to be done beyond the point where the electron stream is collected.
It should be noted that the problem of physical length is most acute with extremely low frequency traveling wave devices, e.g., traveling wave tubes which operate in the frequency spectrum between 60 and 300 megacycles. The low frequency traveling wave tube cannot simply be scaled from higher frequency models. With a direct scaling of higher frequency models, the indication would be that a typical Watt 60 megacycle tube might be 20 or 30 feet in length. Such a tube is not practical and the tube dimensions must be reduced by arranging the various tube elements in such a way that the required power and gain can be obtained in a length of not over 2 to 3 feet. Since the length of structure required to obtain a broad band tapered impedance match is directly related to wave length, in low frequency tubes the input and out-- put matches, which generally require a minimum of near- When a solenoid is used, an
typical half wave length of a helical slow wave transmission line at 60 megacycles is approximately 4 inches. If the tube is on the order of 24 inches long, the matching length represents about 30% of tube length at-this frequency. If the tapering portion of the slow wave circuit is 'done prior to collection of the electron stream, and the portion of the slow wave circuit in the impedance match area is substantially ineffective in providing interaction between the electron stream and the radio frequency waves, then the additional half a circuit wave length may be considered substantially wasted and the electron stream and tube are required to be at least half a circuit wave length longer.
Accordingly it is another object of this invention to provide means for reducing the length of the high frequency energy interchange device to a minimum, which means includes means for simultaneously matching the impedance of a slow wave transmission line to a fast wave transmission line and a means for collecting electrons from the electron stream.
In carrying out the present invention, a tapered impedance matching section is provided between the slow wave transmission line of a traveling wave energy interchange. device and a fast wave output transmission line which output tapered impedance match is accomplished by providing an electron collector and impedance match along the output end of the slow wave transmission line. The physical size and position of the match-collector are arranged in such a manner that electrons from the stream are collected near the beginning of the impedance taper.
The novel features which are believed to be characteristic of this invention are specifically set forth in the appended claims. The invention itself, however, both as to its organization and method of operation, together with further objects and advantages, may best be understood by reference to the following description taken in connection with the accompanying drawings in which:
Figure l is a central, vertical, longitudinal section through a high frequency energy interchange device embodying one form of the present invention;
Figure 2 is a transverse section through the tubular body of the device taken on line 2-2 of Figure 1;
Figure 3 is a side elevation showing one end of the high frequency energy interchange device with the envelope broken away to show only the slow wave struc ture and the collector-impedance match;
Figure 4 is a central, vertical, longitudinal section taken through a part of a high frequency energy interchange device employing another embodiment of the present invention;
Figure 5 is a cross sectional view of the device of Figure 4 taken along section lines 55;
Figure 6 is a perspective view showing the impedance matching and electron collecting member utilized in the energy interchange device illustrated in Figure 4;
Figure 7 is a partially broken away perspective view of still another energy interchange device which employs the present invention; and
Figure 8 is a vertical longitudinal section of the embodiment of Figure 7.
Referring specifically to Figure 1 of the drawing, a traveling wave tube 10 is provided with a long cylindrical (circular cylinder) envelope 11 which is evacuated and sealed. The envelope 11 houses an electron stream producing electron gun 12 at one end which produces and directs a hollow cylindrical stream of electrons 13 down the length of the envelope 11. The envelope 11 also encloses a slow wave transmission line 14 which is illustrated as being a helical strip of conducting material, and an electron collector and impedance matching member 15. The electron collector and impedance matching member 15 is positioned at the opposite end of the electron tube from the electron gun 12, and the slow wave transmission line extends substantially throughout the region between the extreme outer end of the collector 1-5 4 and the electron gun 12. The physical configuration and relative location of the slow wave transmission line 14, the electron stream 13, the collecting and impedance matching member 15, and the envelope 1]. may best be seen by an inspection of Figures 2 and 3 in connection with Figure 1.
With the arrangement just described, the electron stream 13 produced by the electron gun 12, is directed down the length of the interaction region in close proximity to the slow wave transmission line 14. Residual energy in the electron stream is collected on the collector and impedance matching member 15. Thus, the electron stream 13 and electromagnetic waves propagated down the slow wave transmission line 14 interact to provide gain or amplification in the fashion typical to traveling wave tubes. That is to say that the radio frequency waves propagated along the transmission line 14 interact with electrons in the electron stream 13 to cause a redistribution in the form of partial bunching along the stream. As the wave and stream travel substantially synchronously along the helix 14, the inverse phenomenon occurs and the bunched stream induces fields and cur rents upon the helix. The amplitude of the radio frequency waves increases along the helix because the electron stream gives up more energy to the helix than it abstracts therefrom. Consequently an amplification of the radio frequency waves on the helix takes place.
Much of the traveling wave tube illustrated is shown somewhat sketchily. It is felt that more detail is not necessary since many of the elements of the traveling wave tube are common to traveling wave tubes in general and are not novel per se and further, the particular tube design shown is illustrated and discussed in a paper entitled A C-W UHF TWT Power Amplifier of Extended Band Width, by Ward A. Harman, published on pages 36 through 40, inclusive, of the 1957 Proceedings of the National Conference on Aeronautical Electronics, sponsored by the Institute of Radio Engineers, on May 13, 14 and 15, 1957, in Dayton, Ohio. For example, the electron gun 12 which produces the hollow electron stream 13 is illustrated in block form since it is a conventional hollow stream gun known in the art as a Pierce type gun for rectilinear flow. The Harman article supra illustrates and describes the electrode and gun configuration on page 39 and it is felt a detailed description of the particular gun is not warranted. This is particularly true since any hollow stream electron gun could be used in the particular application. Other hollow stream guns which might be used are illustrated and described on pages through 163 of the book by Willis W. Harman entitled Fundamentals of Electronic Motion published by the McGraw-Hill Book Company 1953.
A series of conductive leads 16 are brought into the envelope 11 and connected to various electrodes (not shown) of the gun 12 in order to establish the appropriate electrode potentials to cause the formation and projection of the electron stream 13 down the axis of the device 10. Projecting tabs 17 extend outwardly from the outer periphery of the gun and rest against the inner wall 11 of the vacuum tube 10 and are provided in order to center the gun 12 within the vacuum tube and help hold it in position The conductive leads 16 also help hold the gun 12 in position.
In order to prevent space charge of the electrons in the stream 13 from spreading them to such an extent that they move out of the interaction region and intercept the slow wave circuit 14, it is necessary to provide some focussing means. Focussing is provided by producing a magnetic field axially along the structure. This is typically accomplished by providing a long annular solenoid which surrounds the entire tube. To simplify the present drawing and description, the magnetic field producing solenoid is not illustrated.
As illustrated, the helical transmission line 14 is co axially positioned within the glass envelope 11 by means of glass spacing rods 25 which are spacedequidistant inside the glass envelope 11 in such a manner that they extend longitudinally along the wall over the region occupied by the helix 14. The particular main circuit or beam helix 14 illustrated is designed to operate in the UHF band between approximately 60 and 300 megacycles. As was previously indicated, it is not practical to scale the circuit length from higher frequency models. For the band of frequencies desired, a circuit length of approximately 2 feet was found to be practical with the thin hollow stream of electrons 13 located very close to the circuit.
Radio frequency waves are introduced onto the circuit 14 by means of a conductor 18 brought in to the vacuum tube 11 at the gun end of the tube and the amplified energy is abstracted from the beam helix by means of a coaxial cable 19 near the opposite end of the tube 11. As illustrated, the coaxial cable 19 has an outer conductor 20 connected to the collector 15 and a central inner conductor 21 connected directly to the last turn of the beam helix 14. The interior of the coaxial transmission line 19 is provided with a dielectric window 24 which allows propagation of radio frequency energy down the line but provides a vacuum tight seal.
Reflections of radio frequency energy from the output end of the beam helix must be kept to a minimum if the operation of the high frequency energy interchange device is to have the efiiciency desired and be stable. Therefore, the impedance of the relatively high impedance beam helix 14 (on the order of 400 ohms) is matched to the relatively low impedance coaxial cable 19 (on the order of 50 ohms) using the collectorimpedance match member 15. It is well known that matching two impedances of such disparate values may be accomplished by providing a section wherein the impedance varies continuously, or at least in very small steps, between the two extreme values. This arrangement is known as a tapered impedance or tapered transmission line. Common taper configurations, that is, common ways of varying the impedance between the two values to be matched with distance along the transmission line, are exponential, hyperbolic, parabolic, and cosine. These examples of tapered transmission line impedances may be found in many publications. For example, the hyperbolic line is described in Proceedings of the IRE, volume 41, No. 11, November 1953 in an article by Herbert J, Scott entitled The Hyperbolic Transmission Line as a Matching Section, page 1654, the parabolic transmission line is described in an article having the title Parabolic Transmission Line by R. F. H. Yang in Proceedings of the IRE, volume 43, No. 8, August 1955 at page 1010 and the cosine line may be found in an article by C. O. Lund entitled A Broadband Transition From Coaxial Line to Helix, volume 11, No. 1 of the RCA Review, March 1950 at pages 133 through 142.
The impedance matching and electron collector member 15, which is used to match the impedance between the slow wave helical transmission line 14 and the output coaxial cable 19 is substantially ogival in shape. The collector member is inserted within the slow wave transmission line 14 in such a manner that its axis of revolution, or its central axis, is coincident with the longitudinal axis of the helical transmission line 14 and evacuated envelope 11. The external configuration of the tapered impedance matching member is shaped so that the impedance of the transmission line 14 varies over the matching portion in an exponential cosine fashion as described in the Lund article supra. As previously indicated, the external configuration of the matching section may be varied in any way to obtain any of the desired impedance tapers described in the articles cited above. In any event, the fact that the matching member is a frustum is not crucial since the nose portion of the member is far enough removed from the transmission line 14 that it does not effect the impedance appreciably.
The impedance matching collector member 15 is held in position within the vacuum envelope 11 by means of a cylindrical supporting section 23 which is coaxially arranged and fixed to a disk shaped annular back wall member 22 which extends inwardly from the periphery of the back or large end of the collector 15. The cylindrical supporting member 23 for the collector 15 is held in the glass envelope 11 by a vacuum tight seal around its outer periphery. Thus the entire matching member 15 is held in position within the envelope and its interior is open to the atmosphere to provide a large cooling surface so the residual energy of the electron stream does not overheat the collector 15. The open interior of collector 15 provides space for a coolant to be circulated without affecting the electrical design of the device where it is necessary to provide additional cooling.
From an inspection of Figure 1, it may be seen that the hollow electron stream 13 is collected on the front portion of the tapered impedance matching section, thus allowing most of the impedance matching to be done beyond the point of collection of electrons from the stream. This arrangement eliminates the necessity of providing a separate collector beyond the helical slow wave transmission line 14 and a separate impedance matching section around the helix; thus, substantially the full length of the electron stream is available for interaction with the slow wave structure 14. As a result,
the region which must be occupied by an electron stream focussing field is reduced to a minimum. This means that the amount of equipment required to produce this field is also reduced to a minimum, In contrast with this arrangement, matching by conventional means is accomplished over a region which includes both the transmission line and the electron stream. Consequently, the slow wave transmission line impedance is lowered over the region where the maximum transfer of energy from the electrons to the circuit would otherwise take place.
The arrangement illustrated allows the full impedance of the slow wave transmission line to be maintained over nearly the entire length of the electron stream, thus preventing possible degradation in efficiency as a result of reducing transmission line impedance over the final output section of the high frequency energy interchange device.
Figures 4, 5 and 6 illustrate a portion of a high frequency energy interchange device 30 employing another embodiment of the invention. Only the collector end of a high frequency energy interchange device 30 is illustrated in this figure in order to simplify the description and drawing.
As illustrated, the energy interchange device 30 includes a cylindrical or tubular metallic envelope 31 which is evacuated and sealed. The envelope 31 encloses a helical slow wave transmission line 32, an electron collector and impedance matching member 33 which surrounds the collector end of the slow wave transmission line 32,
and an electron stream producing electron gun (not' energy in the electron stream is collected on the colector' member 33. Thus, the interaction region for the device 30 is outside of the helical transmission line 32. However, the electron stream 34 and electromagnetic waves propagated down the slow Wave transmission line 32 interact to provide gain or amplification in the same manner described with respect to the device 10 of Figure The helical slow wave transmission line .32 is wound on I a supporting dielectric cylinder 35 which is also utilized to hold the helix in Position within the evacuated envelope 31. An annular groove 36, which is concentric with the outer wall of the envelope and just large enough to hold one end of the dielectric helix supporting cylinder 35, is provided in the end wall 37. The end of cylinder 35 is then positioned in the annular groove 36 so that the helix is held coaxially within the evacuated envelope 31. The impedance matching and electron collecting member 33 is positioned coaxially with respect to the circuit helix 32 and externally thereof so that it collects the electrons from the stream 34 near the output end of the device 30. The collector matching member 33, best seen in Figures 4 and 6, has a shape designed to give the desired impedance taper at the output end of the slow wave transmission line 32 as described in connection with the slow wave transmission line 14 in the embodiment illustrated in Figure 1. The shape of the matching member is generally that of the bell or horn of a trumpet. It does not necessarily fit any shape derived from known geometrical figures; however, as illustrated, it closely represents the frustum of a hyperboloid of revolution. The important point is that the open end (i.e., the end having the largest diameter) of the matching member 33 is directed toward the electron gun end of the device 30. In other words, the end of the impedance matching member which is closest to the electron gun is farthest away from the transmission line 32 so that it has the least effect upon the impedance of the line and the end of the matching member 33 which is nearest the collector end of the tube is very close to the transmission line 32 so that it has the maximum effect on the impedance of the line and reduces the impedance to some value which corresponds to the impedance of the particular fast wave transmission line 38 which abstracts power from the device and for which the transmission was designed.
In the design illustrated, the impedance matching and collector member 33 is held in position in the envelope 31 at both ends. The largest end of the impedance matching member 33 is held in position by the tubular envelope 31. This is accomplished by making the outer circumference of the open end of the matching member 33 of such a size as to fit closely within the inner periphery of the cylindrical envelope 31. The smaller end of the matching member 33 is inserted in an annular groove 43 which is concentric with the outer wall of the evacuated envelope 31. Thus, the impedance matching member is held in position within the evacuated envelope 31 and both ends may be brazed to the metallic wall to form a seal. If such seals are provided, a coolant may be circulated around the external surface of the collector member 33 without affecting operation of the device.
The particular fast wave transmission line 38 used to abstract power from the device 30 is a conventional coaxial transmission line which has an outer conductive sheath 39 and an inner conductor 40 separated by a dielectric insulation 42. The coaxial transmission line is also provided with a dielectric window 41 which acts as a seal to prevent deterioration of the vacuum within the energy interchange device 39 and to transmit electromagnetic waves abstracted from the high frequency energy interchange device 30.
The coaxial cable 38 is brought into the energy interchange device 30 through the end wall 37 and the collector matching member 33. The outer conductive sheath 39 of the coaxial cable 38 is electrically connected to both the envelope 31 and the collector impedance match member 33 while the inner conductor 40 is connected to the helix 32. Thus, power is abstracted from the high frequency energy interchange device 30 by the fast wave transmission line 38.
From an inspection of Figure 4, it may be seen that the hollow electron stream 34, like the hollow stream 13 illustrated in Figure 1, is collected on the front portion of the tapered vimpedancematching section, thus a lowing most of the impedance matching to be done beyond the point of collection of electrons from the stre;m. This arrangement eliminates the necessity of providing a separate collector beyond the helical slow wave transmission line 32 and a separate impedance matching section. Consequently, substantially the full length of the electron stream 34 is available for interaction with the slow wave structure 32. As a result, the region which must be occupied by an electron stream focussing field is reduced to a minimum. This means that the amount of equipment required to produce this field is also reduced to a minimum. In contrast with this arrangement, matching by conventional means is accomplished over a region which includes both the transmission line and the electron stream. Consequently, the slow wave transmission line impedance is lowered over the region where the maximum transfer of energy from the electrons to the circuit would otherwise take place.
The arrangement illustrated in Figures 4, 5 and 6 also allows the full impedance of the slow wave transmission line to be maintained over nearly the entire length of the electron stream, thus preventing possible degradation in efficiency as a result of reducing transmission line impedance over the final output section of the high frequency energy interchange device.
Figures 7 and 8 illustrate the invention as appplied in a linear sheet stream type high frequency energy interchange device 45. The elements utilized in the device 45 correspond to the elements in the devices illustrated in Figures 1 and 4 and the basic interaction mechanism of the apparatus disclosed in Figures 7 and 8 does not differ in any fundamental respects. However, the construction of the elements of the devices are somewhat different. Consequently, the impedance matching and electron stream collecting members differ in geometrical configuration.
The device 45 includes an enclosed and evacuated envelope 46 having a rectangular cross section. Envelope 45 encloses a transmission line 47 of the type referred to as a zig-zag slow wave circuit, a sheet stream producing electron gun 48 at one end, and an impedance matching and electron-collecting member 49 at the opposite end of the device. The electron gun 48 pro duces and directs a sheet-like stream of electrons 50 down the length of the envelope 46 beneath and in close proximity to the zig-zag slow wave circuit 47 and the electrons are collected at the opposite end of the device on the collector and matching member 49. Thus, the electron stream 5i and the electromagnetic Waves propagated down the zigzag slow wave circuit 47 interact to produce amplification in a manner similar to that described with respect to the device 1% of Figure l.
The electron gun 48 is illustrated rather diagramatically since it is a conventional gun for producing rectilinear electron flow. The gun includes a cathode member 51 with an electron emissive surface 52, two pairs of electron focussing and directing electrodes 53 and 54, respectively, and heater elements which are not shown. Each of the pairs of electron focussing and directing electrodes 53 and 54 includes two substantially planar, rectangular conductive plates spaced far enough apart to allow the rectilinear stream of electrons 50 to pass between them and are sloped to insure that the electron accelerating and directing electric fields therebetween have the desired configuration. The design considerations for a gun of the type illustrated are discussed in the book entitled Theory and Design of Electron Beams 2nd edition by J. R. Pierce, Van Nostrand Company, Inc., New York (1954) in section 10.1 at page 174 et seq. The particular type gun illustrated in Figures 7 and 8 is illustrated in the Pierce book in Figure 10.5 on page 178. Leads are brought in through the outer end wall of the device to energize the gun electrodes. Only two such leads are illustrated, but other leads nc ma lyn v drd t est ish ele t pds p e 9. tials. A magnetic focussing field is also provided to focus the electron stream 50. This is typically done by a solenoid (not shown) external to the device.
The substantially planar zig-Zag slow wave circuit 47 is suspended with its plane generally horizontal and parallel to the plane of the sheet electron stream 50 by means of insulating supporting strips 55 which extend down the full length of the energy interchange device 45. A pair of strips 56 is provided along each side of the device; however, it is not convenient to illustrate both pairs of strips in either Figures 7 or 8. The strips are all identical, are generally L-shaped in cross section and are arranged in the same general manner on opposite sides of the device. As may best be seen in Figure 7, the pair of slow wave circuit supporting insulating strips 56 are arranged along one side wall of the envelope 46 in such a manner that the legs of the Us mate to support one edge of the slow wave circuit 47.
The particular device illustrated operates as a forward wave amplifier. As a consequence, the radio frequency energy is introduced onto the slow wave circuit 47 by means of a coaxial transmission line 57 at the gun end of the device and the amplified radio frequency energy is abstracted by means of the coaxial transmission line 58 at the collector end. The input coaxial transmission line 57 includes a center conductor 59 which is connected to the input end of the slow wave transmission line and an outer conductive sheath 60 Which is brought into the energy interchange device and connected to an input impedance matching conductive member 62. In a corresponding fashion, the output coaxial conductor 58 includes an inner conductor 61 which is connected directly to the slow wave transmission line 47 at its output end and an outer conductive sheath 65 which is connected to the output impedance matching and collector member 49.
Impedance matching members 49 and 62 are of substantially identical geometrical configuration although, as illustrated, the size of the two members may differ. The portion of the members which accomplishes the matching function is the conductive surfaces 63 and 64- respectively, which are best described as having generally parabolic shapes when viewed from the side (see Figure 8). As was the case with the impedance matching members described in connection with previous embodiments, the shape is not necessarily derived from any known geometrical figures but is designed to give the desired transition in impedance between the transmission lines under consideration. The proper impedance match is accomplished between the coaxial transmission line 57 at the gun end of the tube by positioning the matching member 62 in such a manner that its conductive surface is near the zigzag transmission line 47 near the gun end and slopes away from the circuit. Thus, for most of the frequency range of interest, the impedance of the slow wave transmission line 47 is low (about 50 ohms) near the gun end and is approximately that of the coaxial transmission line 57.
Conversely, thhe conductive surface 63 of the collector impedance match member 49 is relatively far from the slow wave circuit 47 at the end Where it collects electrons and is very near the slow wave circuit near the coaxial transmission line 58. Thus, the electron stream 50 is collected on the front portion of the collector 49 where the collector has little effect on the impedance of the slow wave circuit 47. Consequently, most of the impedance matching is done beyond the point of collection of electrons in the stream. As a result, substantially the full length of the stream 50 is available for interaction with the slow wave circuit 47.
Both of the matching members 49 and 62 are illustrated as solid members. This is done because it is a simple construction and such members can easily be brazed to the walls of the envelope 46. However, the
matching members may be made hollow to provide for coolant or of any other desired construction.
The high frequency energy interchange devices 10, 30 and 45 are all illustrated as forward wave amplifiers. It is to be particularly understood that the principles set forth are equally applicable to backward Wave ampli-t tiers and forward and backward wave oscillators. It should also be understood that the invention is equally applicable to cylindrical devices as well as the linear models illustrated.
While particular embodiments of the invention have been illustrated and described, it will, of course, be understood that the invention is not limited thereto, since many modifications both in the circuit arrangements and in the instrumentalities employed may be made. It is contemplated that the appended claims will cover any such modifications as fall within the true spirit and scope of the invention.
What I claim is new and desire to secure by Letters Patent of the United States is:
l. A high frequency energy interchange device including an evacuated envelope, a slow wave transmission line positioned within said envelope, an electron stream producing means positioned at one end of said evacuated envelope for producing a stream of electrons in the axial direction within said evacuated envelope and in close proximity to said slow wave transmission line, input and output fast wave transmission lines connected to said slow Wave transmission line to introduce radio frequency energy thereon and abstract radio frequency energy therefrom respectively, and an impedance matching electron stream collecting means positioned within the end of said evacuated envelope opposite the electron stream producing means and in the path of the electron stream, said stream collecting means having a collecting surface coextensive with a portion of said transmission line which surface is closest to said transmission line at its end which is furthest removed from said electron stream producing means and tapers away from said transmission line at its end which is nearest said electron gun producing means in such a manner that the electron stream is intercepted along the length of the said stream collecting means whereby the impedance of said slow wave transmission line is gradually reduced and residual energy in said electron stream is dissipated in the region where the impedance is reduced.
2. A high frequency energy interchange device including an evacuated envelope, a slow wave transmission line positioned within said envelope, an electron stream producing means positioned at one end of said evacuated envelope for producing a stream of electrons in the axial direction Within said evacuated envelope and in close proximity to said slow wave transmission line, input and output fast wave transmission lines connected to said slow wave transmission line to introduce radio frequency energy thereon and abstract radio frequency energy therefrom respectively, and an elongated impedance matching electron collecting member positioned in the path of the electron stream near said slow wave transmission line within the end of said envelope opposite the electron stream producing means, said impedance matching electron collecting member extending along the length of said slow wave transmission line at least one half circuit wave length for the lowest frequency in the band of frequencies under consideration and having an electron collecting surface which is farthest from said slow wave.
transmission line at its end nearest the electron stream producing means and tapers toward said slow wave transmission line thereby to gradually reduce the impedance of said transmission line and intercept the electrons from said stream along its length.
3. A high frequency energy interchange device including an evacuated envelope, a coiled slow wave transmission line positioned within said envelope along the longitudinal axis thereof,
an electron stream producing means positioned at one end of said evacuated envelope for producing a stream of electrons in the axial direction within said evacuated envelope and said coiled slow wave transmission line, input and output fast wave transmission lines connected to said coiled transmission line to introduce radio frequency energy thereon and abstract radio frequency energy therefrom respectively, and an impedance matching electron stream collecting means coaxially positioned adjacent the end of said coiled slow wave transmission line opposite the electron stream producing means, said impedance matching means arranged to extend over a portion of the same region as said transmission line and have its end which is closest to said electron producing means the greatest distance from said transmission line for performing the functions of gradually reducing the impedance of said coiled slow wave transmission line and dissipating residual energy in said electron stream.
4. A high frequency energy interchange device including an evacuated envelope, a coiled slow wave transmission line positioned within said envelope along the longitudinal axis thereof, an electron stream producing means positioned at one end of said evacuated envelope for producing a stream of electrons in the axial direction within said evacuated envelope and said coiled slow wave transmission line, input and output fast wave transmission lines connected to said coiled transmission line to introduce radio frequency energy thereon and abstract radio frequency energy therefrom respectively, and an elongated impedance matching electron collecting member positioned within the end of said helical transmission line opposite the electron stream producing means and extending at least one half circuit wave length for the lowest frequency in the band of frequencies under consideration, said impedance matching electron collecting member having an externai surface of revolution which has its smallest diameter nearest the electron stream producing means.
5. A high frequency energy interchange device including an evacuated envelope, a coiled slow wave transmission line positioned within said envelope along the longitudinal axis thereof, an electron stream producing means positioned at one end of said evacuated envelope for producing a stream of electrons in the axial direction within said evacuated envelope and outside said coiled slow wave transmission line, input and output fast wave transmission lines connected to said coiled transmission line to introduce radio frequency energy thereon and abstract radio frequency energy therefrom, respectively, and an elongated impedance matching electron collecting member positioned around the end of said helical transmission line opposite the electron stream producing means and extending at least one half circuit wave length for the lowest frequency in the band of frequencies under consideration, said impedance matching electron collecting member having a collecting surface of revolution which has its largest diameter nearest the electron stream producing means.
6. A high frequency energy interchange device including an evacuated envelope, a substantially planar slow wave transmission line positioned within said envelope along the length thereof, an electron stream producing means positioned at one end of said evacuated envelope for producing a sheet stream of electrons in the axial direction within said evacuated envelope in close proximity to said slow wave transmission line, input and output fast wave transmission lines connected to said slow wave transmission line to introduce radio frequency energy thereon and abstract radio frequency energy therefrom respectively, and an elongated impedance matching electron collecting member positioned adjacent the end of said slow wave transmission line opposite the electron stream producing means in the path of the stream and extending along said slow wave transmission line at least one half circuit wave length for the lowest frequency in the band of frequencies under consideration, said impedance matching electron collecting member having an electron collecting surface which is farthest from said slow wave transmission line nearest the electron stream producing means and tapers toward said transmission line.
7. A high frequency energy interchange device including in combination an evacuated envelope, a substantially planar slow wave transmission line positioned within said envelope, an electron stream producing means for producing a sheet stream of electrons in the axial direction within said envelope in close proximity to said slow wave transmission line, input and output fast wave transmission lines connected to said slow wave transmission line to introduce radio frequency energy thereon and abstract radio frequency energy therefrom respectively, and an impedance matching electron stream collecting means positioned within the end of said envelope opposite the electron stream producing means for performing the functions of gradually reducing the impedance of said slow wave transmission line and dissipating residual energy in said electron stream, said electron stream collecting means including a collecting surface coextensive with the portion of said slow wave transmission line which surface is closest to said transmission line at its end which is furtherest removed from said electron stream producing means and tapers away from the transmission line at its end which is nearest said electron stream producing means.
8. In combination in a high frequency energy interchange device, an evacuated envelope, a helical slow wave transmission line coaxially positioned within said envelope, an electron stream producing means for producing a hollow stream of electrons in the axial direction within said helical transmission line in close proximity thereto, input and output fast wave transmission lines connected to said helical transmission line to introduce radio frequency energy thereon and abstract radio frequency energy therefrom, respectively, and an elongated impedance matching electron collecting member positioned within the end of said transmission line opposite said electron gun, said impedance matching member having a length of at least one half circuit wave length for the lowest one of the band of frequencies under consideration and having a surface of revolution which has its end with the smallest diameter directed toward said electron gun and peripheral dimensions of such proportions that electrons from the stream are collected adjacent a high impedance region of said slow wave transmission line.
9. In combination in a high frequency energy interchange device, an evacuated envelope, a helical slow wave transmission line coaxially positioned within said envelope, an electron stream producing means for producing a hollow stream of electrons in the axial direction within said envelope in close proximity to said slow wave transmission line, input and output fast wave transmission lines connected to said helical transmission line to introduce radio frequency energy thereon and abstract radio frequency energy therefrom respectively, and an elongated impedance matching electron collecting member coaxially positioned within the end of said envelope opposite said electron gun, said impedance matching member extending along the length of said slow wave transmission line a distance of at least one half circuit wave length for the lowest one of the band of frequencies under consideration and having a surface of revolution which has its end which is farthest away from said slow wave transmission line directed toward said electron gun and peripheral dimensions of such proportions that electrons from the stream are collected adjacent a high impedance region of said slow wave transmission line.
10. In combination in a high frequency energy interchange device, an evacuated envelope, a slow wave transmission line positioned within said envelope, an electron stream producing means for producing a sheet stream of electrons in the axial direction within said envelope in close proximity to said slow wave transmission line, input and output fast wave transmission lines connected to said slow wave transmission line to introduce radio frequency energy thereon and abstract radio frequency energy therefrom respectively, and an elongated impedance matching electron collecting member positioned adjacent the end of said slow wave transmission line opposite said electron gun, said impedance matching member having a length of at least one half circuit wave length for the lowest one of the band frequencies under consideration and having a surface which varies in distance from said slow wave transmission line in such a manner that its end which is directed toward said electron gun is farth est removed from said slow wave transmission line and electrons from the stream are collected adjacent a high impedance region of said slow wave transmission line.
11. In a high frequency energy interchange device of the type which depends upon the interaction of an electron stream produced by an electron gun with electromagnetic waves propagated down a slow wave transmission line adjacent the electron stream, an electron stream collecting tapered impedance matching member located within the end of the device opposite the electron stream producing gun with the portion farthest removed from the transmission line directed toward the gun and extending along the length of the transmission line.
12. A combination electron collector impedance matching member for use in a high frequency energy interchange device which depends upon the interaction of an electron stream with electromagnetic waves propagated down a transmission line in close proximity to the electron stream, the said electron collecting impedance matching member positioned adjacent the slow wave transmission line and comprising a conductive member having a tapered surface which extends at least one-half circuit wave length along the transmission line with its end which is the greatest distance away from the transmission line directed toward the source of electrons.
13. In a high frequency energy interchange device of the type which depends upon the interaction of an electron stream produced by an electron gun with electromagnetic waves propagated down a helical transmission line surrounding the electron stream, a substantially ogival shaped electron stream collecting impedance matching member located within the end of the helical transmission line opposite the electron stream producing gun w.th the portion having the smallest diameter directed toward the gun.
14. A combination electron collector impedance matching member for use in a high frequency energy interchange device which depends upon the interaction of a hollow electron stream with electromagnetic waves propagated down a helical transmission line inside the electron stream, the said electron collecting impedance matching member comprising a conductive member having a tapered surface of revolution extending at least one-half circuit wave length around one end of the helical transmission line with its largest end directed toward the source of electrons.
15. A high frequency energy interchange device including an evacuated envelope, a coiled slow wave transmission line positioned within said envelope along the longitudinal axis thereof, an electron stream producing means positioned at one end of said evacuated envelope for producing a stream of electrons in the axial direction with said evacuated envelope and said coiled slow wave transmission line, input and output fast wave transmission lines connected to said coiled transmission line to introduce radio frequency energy thereon and abstract radio frequency energy therefrom respectively, and an elongated impedance matching electron collecting member having an external surface of revolution which is generally ogival positioned in the end of said helical transmission line opposite the electron stream producing means in such a manner that the end of reduced diameter is directed toward said electron stream producing means, said impedance matching member having a length corresponding to at least one-half circuit wave length for 14 the lowest frequency of the band of frequencies under consideration.
16. A high frequency energy interchange device including in combination an evacuated envelope, a helical slow wave transmission line coaxially positioned within said envelope, an electron stream producing means for producing a hollow stream of electrons in the axial direction within said helical transmission line in close proximity thereto, input and output fast wave transmission lines connected to said helical transmission line to introduce radio frequency energy thereon and abstract radio frequency energy therefrom respectively, and a substantially ogival shaped conductive impedance matching electron stream collecting means positioned within the end of said helical slow wave transmission line opposite the electron stream producing means for performing the functions of gradually reducing the impedance of said helical slow wave transmission line and dissipating residual energy in said electron stream.
17. In combination in a high frequency energy interchange device, an evacuated envelope, a helical slow wave transmission line coaxially positioned within said envelope, an electron stream producing means for producing a hollow stream of electrons in the axial direction within said helical transmission line in close proximity thereto, input and output fast wave transmission lines connected to said helical transmission line to introduce radio frequency energy thereon and abstract radio frequency energy therefrom respectively, and an elongated impedance matching electron collecting member having a substantially ogival conductive surface positioned within the end of said transmission line opposite said electron gun with its end having the smallest diameter directed toward said electron gun, said impedance matching member having a length of at least one-half circuit wave length for the lowest one of the band of frequencies under consideration and peripheral dimensions of such proportions that electrons from the stream are collected adjacent a high impedance region of said slow wave transmission line.
18. In a high frequency energy interchange device of the type which depends upon the interaction of an electron stream produced by an electron gun with electromagnetic waves propagated down a helical transmission line surrounding the electron stream, an electron stream collecting impedance matching member having a shape defined by the frustum of an ogive located within the end of the helical transmission line opposite the electron stream producing gun with the portion having the smallest diameter directed toward the gun.
19. A high frequency energy interchangedevice including an evacuated envelope, a helical slow wave transmission line positioned coaxially within said envelope, a hollow electron stream producing means positioned at one end of said evacuated envelope for producing a stream of electrons in the axial direction within said evacuated envelope and external to said slow wave transmission line, input and output fast wave transmission lines connected to said helical transmission line to introduce radio frequency energy thereon and abstract radio frequency energy therefrom respectively, and an elongated impedance matching electron collecting member having an internal surface of revolution which is substantially defined by the frustum of a hyperboloid positioned surrounding the end of said helical transmission line opposite the electron stream producing means in such a manner that the end of greatest diameter is directed toward said electron stream producing means, said impedance matching member having a length corresponding to at least one-half circuit wave length for the lowest frequency of the band of frequencies under consideration.
20. In combination in a high frequency energy interchange device, an evacuated envelope, a helical slow wave transmission line coaxially positioned within said enaseaeao 15 velope, an electron stream producing means for producing a hollow stream of electrons in the axial direction within said helical transmission line in close proximity thereto, input and output fast wave transmission lines connected to said helical transmission line to introduce radio frequency energy thereon and abstract rad-i0 frequency energy therefrom respectively, and an elongated impedance matching electron collecting member having a conductive surface defined by the frusturn of an ogive positioned within the end of said transmission line 0pposite said electron gun with its end having the smallest diameter directed toward said electron gun, said impedance matching member having a length of at least one-half circuit wave length for the lowest one of the band of frequencies under consideration and peripheral dimensions of such proportions that electrons from the stream are collected adjacent a high impedance region of said slow wave transmission line.
References Cited in the file of this patent UNITED STATES PATENTS (3d addition to 985,536)
UNITED STATES PATENT OFFICE CERTIFICATION OF CORRECTION Patent No, 2,962,620 November 29, 1960 Ward A Harman It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.
Column 13, lines 22 and 23, strike out "and extending along the length of the transmission line" and insert the same after "gun" in line 21, same column.
Signed and sealed this 2nd day of May 1961.,
(SEAL) Attest:
ERNEST Wn SWIDER DAVID L LADD Attesting Officer Commissioner of Patents
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US3359452A (en) * 1965-10-14 1967-12-19 Quentin A Kerns Resonator for supporting non-sinus-oidal preiodic waveforms

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US2578434A (en) * 1947-06-25 1951-12-11 Rca Corp High-frequency electron discharge device of the traveling wave type
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FR985536A (en) * 1949-02-22 1951-07-19 Csf Wave propagation amplifier tube with magnetic field produced by a current flowing in an axial conductor
US2794143A (en) * 1949-07-12 1957-05-28 Csf Progressive wave tube comprising an output cavity and a drift space
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